The intent of this research project is to utilize tissue samples from spontaneous abortions and blood samples from their parents to answer four questions: 1) How do chromosome abnormalities arise? 2) Is there a correlation between the stage of origin of a chromosome abnormality and the phenotype of the abnormal conception? 3) What is the importance of chromosome abnormalities that are restricted to certain tissues (e.g. placenta)? 4) What is the incidence of chromosome abnormalities in spontaneous abortion?